Boiler and domestic hot water tank

[PhilNH5]

Folks,
I have a question about the topic. I have always had a gas furnace and a stand-alone hot wat heater in my prior houses. The house I live in now came with a boiler for baseboard hot water heat and a tankless coil for domestic hot water.
Well the boiler went and yesterday I had it replaced. I opted for an indirect water tank. There is a storafe tank and a pipe goes from the boiler into the tank to heat the domestic hot water.

The boiler guy set the tank for 160F which seems extremely high to me. There is a tempering valve as the hot water pipe leaves the tank. This mixes in cold water so the water at the tap is not 160F.

My question is: Do I need to leave the tank at 160F? The boiler guy said "Yes" to prevent legionaires disease from growing. Well I certainly don't have an answer for that. But in my prior houses we set the water heater to 120F and that always worked well for me. Seems like a waste of energy to heat the tank to 160F for storage and then immediately temper it down for usage.

Oh - the boiler guy is NOT my oil dealer so this is not a gimmick to sell me more oil. (Boy that sounds like I am paranoid).

As always, thanks for any thoughts or advice.

Phil

 

[Mark_in_NH]

Phil,
As I am not a plumber, licensed or otherwise, I can not attest to the actual NH state plumbing code on this. BUT !!
Back some years ago, before I really ventured out on my own. I was working with a licensed plumber and pump installer. He told me Many times that it was a violation of the state plumbing code for a plumber to set the hot water thermostat any higher then 120 F. Once the plumber left, the homeowner could set it anywhere he/she wished.
My suggestion would be to check the NH state plumbing code for verification.
160 F is pretty darned hot, but maybe the boiler installer has learned over the years, that with the mixing valve installed, the temp needs to be set higher so as to get the desired results down stream.

 

[djradz]

Phil, I'm not sure I understand you're whole setup but I'll try to reply to what I do know. Most dishwashers require 140 degree water coming into the dishwasher to clean properly and help disinfect. Would think the clothes wash machine would be something similar. Are you sure the domestic hot water tank is at 160 and not the boiler that's providing the heat. Actually, now that I think of it, 160 would be a little low for a boiler heating system. I think most require something more like 180 to get the air moving through the radiant registers. However, my boiler is also a backup to my wood boiler, and that usually runs around 130 to 160.

 

[PhilNH5]

djradz,
I don't know what the boiler is set at. But there is a thermostat on the domestic hot water storage tank and it is set at 160F. I almost burnt myself on the hot water supply leaving the tank.

This 160F is then mixed with cold water at the tempering valve. The valve is homeowner adjustable so I can have what ever temp I want coming out of the faucet. Again it just seems wasteful to heat the tank to 160F and then immediately temper it down.

The boiler guy has to finish the heating system part of the install. If he is still there when I get home I will talk with him.

Phil

 

[frank_f15]

I AM not sure exactly what your set up is like, but i will tell u that 160 deg. on domestic hwt IS EXTREMLY HIGH. if it was me i would be inclined to check into it further. normally 120 deg. is too hot to keep your hand under, 160 will burn u real good.

 

[PhilNH5]

The storage tank is set at 160F but the household hot water is tempered down to 120F.

Since I am confusing everyone I will try and attach a drawing.

Phil

 

[tbuff]

Phil,

I can't remember if it is a code requirement but most hot water boiler/tank systems are designed to run at temperatures in the 160 - 190 degree range. To set them lower casues the system to run inefficiently. The boiler will be cycling on an off to often. With an oil fired boiler, this will end up costing you much more $$ than heating the tank. You should leave it as is, this is the reason for using the tempering valve to set temperature at the tap. The disease issue is also real though not very common.
If you have a "stone" lined tank which it apppears you probably have, it is very efficient and will not be very expensive to mainttain at temperature.

Sounds like you got a good plumber

 

[PhilNH5]

Steve,
Thank you for the reply. That all makes sense now. In fact I replaced the tankless coil with this storage tank because the boiler cycled on/off for short periods to heat the 4 gallons in the coil.

Again thanks for helping me understand that. And yes I did get a great plumber. Have 3 zones plus now the water tank and it looked like a birdsnest back there. But this guy replaced a lot and ran it all straight and neat. Now even I can follow all the lines.

Phil

 

[cmsedore]

The other reason to do this is because it lets you purchase a smaller indirect tank. The 160 deg water mixing with cold to get you 120 (or 140) buys you about 20% more hot water from the same size tank storing water at the desired output temp.

I have an outdoor wood boiler with a heat exchanger built into the water jacket. The output water temp will exceed 160 degrees sometimes--the tempering valve is a must (and I actually have been toying with putting a second one in series as a backup--I don't want 160+ degree water coming up my DHW system!!!) FWIW, my first tempering valve failed, but it failed "cold", I couldn't get better than about 105 degree water from it.

-Chris